1. Field of the Invention
The present invention generally relates to the fabrication of integrated circuits and, more particularly, to a method for removing masking materials from dielectric materials having a low dielectric constant (hereinafter, low-k materials) during the fabrication of integrated circuits.
2. Description of the Related Art
Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density. The demands for greater circuit density necessitate a reduction in the dimensions of the integrated circuit components.
As the dimensions of the integrated circuit components are reduced (e.g., sub-micron dimensions), the materials used to fabricate such components have a greater impact on the electrical performance of the integrated circuit. For example, low resistivity metal interconnects (e.g., copper and aluminum) provide conductive paths between the components on integrated circuits. The metal interconnects are electrically isolated from each other by an insulating material. When the distance between adjacent metal interconnects and/or the thickness of the insulating material has sub-micron dimensions, capacitive coupling may occur between the metal interconnects, thereby causing cross talk and/or resistance-capacitance (RC) delay and degrading the overall performance of the integrated circuit. In order to reduce capacitive coupling between adjacent metal interconnects, low-k materials (e.g., dielectric constants less than about 4.0) are utilized.
Unfortunately, low-k materials are not easy to process using conventional fabrication techniques. In particular, low-k materials are susceptible to damage during plasma processing, such as plasma processing used to strip masking materials (i.e., photoresist layers) after a feature has been etched into a low-k material layer. For example, when using an oxygen plasma to remove photoresist, the oxygen reacts with and removes carbon and/or hydrogen near the surface of the exposed low-k materials, thereby damaging the low-k material. The alteration of the low-k material results in a low-k shift, wherein the dielectric constant of the material is changed.
In addition, this damage generally leads to further additional processing problems. For example, in a subsequent wet etch step to remove residue, such as a hydrofluoric acid (HF) dip, the damaged low-k material is undesirably removed as well. In fabrication processes such as forming interconnect structures or etching other features into the low-k materials, this causes a condition known as sidewall pull-back. Where less susceptible layers are also present, such as a capping layer that may be disposed over the low-k materials, the non-uniformity of the sidewall profile of the exposed low-k material forming part of the interconnect feature leads to difficulty in subsequent conductive material deposition steps required to complete the interconnect feature, potentially resulting in complete failure of the integrated circuit containing the defective interconnect structure.
Therefore, a need exists for an improved method of removing masking materials from low-k materials.